This chapter summarizes the neurological approaches used to assess the potential long-term effects of drugs on the nervous system of drug abusers. These include the use of neuropsychological assessments, transcranial Doppler (TCD) sonography, and electroencephalographic (EEG) recordings. Neuropsychological procedures are used in an effort to provide an unbiased estimate of the individual's cognitive capacity, and included tests of language skills, attention, memory, and motor skills. TCD allows for the measurements of blood flow in the anterior cerebral and middle cerebral arteries, which supply blood to the cortex. An EEG recording was included in our assessment on marijuana abusers using a sound-attenuated, electronically shielded chamber. These neurological approaches have allowed the detection of various neurological and neurovascular deficits that are associated with the abuse of marijuana.